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The maintenance of bridges and the evolution of an appropriate bridge rating system require the consideration of loads from heavy trucks. These loads can arise from a single overweight truck or multiple trucks simultaneously present, or concurrent, on a bridge. This paper presents a probabilistic modeling approach to assess the frequency and likelihood of observing various bridge loads caused by single and concurrent trucks. The approach used weigh-in-motion (WIM) data collected at or near bridges of interest to identify single and concurrent trucks and their Corresponding loads. The modeling approach was applied to bridges near three WIM stations in Florida. Results showed that in any given month, there was a 100% probability of observing at least one single or concurrent truckload that exceeded twice the minimum weight of a single overweight truck (i.e., exceeded 711,715 N or 160,000 lb). In addition, the probability of observing extreme truckloads was significantly higher when all trucks were considered, as opposed to only overweight trucks. The modeling approach can easily be adapted to the goals of the study and to any region where WIM data are available at or near the bridge(s) of interest. Results generated from the modeling approach provide probabilistic loading input for bridge maintenance planning and truck permitting policy.